Updating user agent formatting

[Chriztiaan]

For context, the current user agent strings are not parsed successfully and end up as "unknown" on the current and last 30 days connected device charts in the new dashboard.

Documented examples:

powersync-dart/1.6.4 Dart/3.4.2 linux
powersync-dart/1.6.4 Dart/3.4.2 android/34
powersync-dart/1.6.4 Dart (flutter-web) Chrome/128 android
powersync-js/1.16.2 powersync-react-native/1.11.0 react-native/0.78 android/34
powersync-js/1.16.2 powersync-web/1.6.0 Chrome/128 android

Proof of success:

Screenshots

[Chriztiaan]

I couldn't see a clear way that we access this currently. For Kotlin we manage a LIBRARY_VERSION variable in the gradle.properties.
Is that a similar mechanism we want to follow?

[simolus3]

This is a good point, I don't think we can automate this with SwiftPM alone. What might work is to:

1. Add a Sources/PowerSync/CurrentVersion.swift with an internal libraryVersion string constant.
2. In the release.yml workflow, update that constant with ${{ github.event.inputs.version }}.
3. Commit that file in the action before creating the tag.